1. Field of the Invention
The present invention relates generally to electrical devices such as sensors and transducers and more particularly to a support arrangement for accurately positioning an electrical device that is molded within a support body; the support arrangement responding to volumetric changes in the material of the support body during molding.
2. Description of the Related Art
Various electrical devices molded within support bodies or housings are known, including current and/or voltage transducers incorporated within porcelain structures or molded within housings. For example, see the Fisher Pierce Series 13000 VIP Sensor.sup.198 and the following U.S. Pat. Nos.: 4,823,022; 4,002,976; 4,775,849; 3,315,147; 4,808,910; 4,700,123; 4,019,167; 3,386,059; 3,187,282; 3,970,932; 3,251,104; and 3,932,810. The arrangements of U.S. Pat. Nos. 4,808,910, 4,700,123, 3,315,147, and 4,775,849 dispose an electrical device within a support housing, but do not encapsulate or pot the electrical device. In U.S. Pat. No. 4,019,167, a transformer is encapsulated within a molded jacket. Connector elements for the transformer leads are incorporated with the jacket. Additionally, a cushion of resilient material (closed-cell foam rubber) surrounds the transformer and is co-extensive with the interior of the jacket. U.S. Pat. Nos. 3,932,810, 4,823,022, and 3,187,282 disclose encapsulated transformers or coils, but do not disclose how the transformers or coils are supported during encapsulation. The arrangements of U.S. Pat. Nos. 3,251,014, 3,386,059, and 3,970,932 are directed to the potting of electrical devices such as coils within an annular channel or cavity of a housing or support insulator. In U.S. Pat. No. 3,386,059, the arrangement also provides for the support of a coil assembly by a tube through which conductors from the coil assembly are routed to the base of the insulator.
While these prior art arrangements may be generally useful, they do not provide an arrangement suitable for the molding of an electrical device within a support body that accurately positions the electrical device during molding and that accommodates for the volumetric changes of the molding compound during molding and curing. For example, where the electrical device is located adjacent the top of a support insulator and is supported with respect to the base of the insulator, it is especially important to provide accurate positioning of the electrical device along with compensation for the volumetric changes of the molding compound and the resultant forces on the electrical device and the supporting arrangement therefor. Further, the molding operations are additionally complicated if the electrical device to be encapsulated includes a centrally defined bore through which a conductor is to be disposed so as to be insulated by the molding material from the electrical device. Additionally, other than by deformation of a cushioning element, the prior art arrangements do not address the encapsulation of an object where the shape factor (volume and overall length) and/or surface characteristics are such that during molding and/or curing, volumetric changes of the molding compound relative to the object produce undesirable stresses. For example, U.S. Pat. No. 4,019,167 provides for some relief of undesirable stresses only via a surrounding layer.